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I noticed some vignetting when I shoot in bright light, see below for an example: Dark area one long edge

This usually occurs then I shoot with with a Sony DSLM (A7II or NEX3N) and a vintage (long focal length) lens. I can be avoided by closing the aperture which leads to longer exposures.

My question is: What is the origin of this issue?

My guesses are that the curtain shutter works really at its limit for these short exposures, as the "shadow" always appears one long edge of the image, or the the sensor is exposed to different amounts of light, due to the influence of a lens hood and the wide aperture.

EDIT: I was able to observe this behaviour again and gathered more information:

  • The shadow always occurs on the top edge of the image (bottom edge of the sensor?) referring to the camera in landscape orientation.
  • It also occurs independently from the direction of incident light.
  • Removing the lens hood has no influence on the phenomenon.

So if we are talking about heavy vignetting, why is it so asymmetric?

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    What is the native mount of the vintage lenses you are using? How are they being adapted to your Sony cameras? – Michael C Oct 7 '18 at 5:15
  • For the shown example a lens with an Exa-bayonet was used. I also experienced it with a Praktika B-mount zoom lens. I use ~20€ worth adapters to Nex/E-mount. – Doochi Oct 7 '18 at 8:44
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The issue is not related to the shutter, or it’d affect all lenses. There’s a similar looking effect caused by too short a shutter exposure with flash, but that’s not what you’re experiencing here as you’re not using flash.

The problem is probably exacerbated by how you’ve mounted the lens to the camera, but it is also related to the lens itself. Some older lenses have heavy vignetting.

As can be seen here, vignetting is affected by aperture: https://m.dpreview.com/reviews/nikon-35-1p8g-n15/3

I believe your camera is crop-sensor? So likely what’s happening is that as you shut down the aperture the vignette is less blurred, and falls outside of the crop sensor.

I think Sony’s lens mount is fairly small which makes it harder to attach vintage lenses (compared to canon’s huge mount which allows non-optical adaptors for almost all lenses). If you’ve got an optical adaptor, that’s more likely to be causing a problem.

As for why it’s always on one side; this might mean you’ve got an inappropriate lens hood - take off the hood to check - or could be due to the lens design. However, it’s more likely related to your adaptor. Probably the adaptor hasn’t positioned the lens correctly.

  • Thank you for the answer! However, I am not convinced about the influence of the adapter yet, as I am using non-optical adaptors. Personally, I guess the hood explanation is right. Unfortunately I was not able to recreate it and try it with and without hood, as this effect only occurs in really bright sun light (as it seems). – Doochi Oct 7 '18 at 10:05
  • Anecdotally, I’ve had problems with some badly made adaptors, which weren’t infinity focus capable. – Dan W Oct 7 '18 at 10:38
  • A Sony A7 II is a full frame camera, not crop sensor. – Eric Shain Feb 2 at 21:27
  • @EricShain good spot. The NEX3N is crop. – Dan W Feb 3 at 16:52
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The effect is caused by the "e-Front Curtain Shut."-option which is activated by default in Sony cameras.

As far as I understand the guide for this option, it is meant to reduce the lag between shutter releases. According to this site, its main benefit is that the camera shake is reduced, as the front curtain does not move and the start of the exposure is controlled electronically.

However, an uneven brightness and other negative effects are documented for its usage with large diameter or third party lenses and short exposure times, see the camera guide.

I tested the deactivation of this option for the conditions I mentioned in the questioned and can ascertain that it fixes the problem.

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